Although inhibin-like activity has been demonstrated in testicular extracts and in fluids derived from the testes and in ovarian follicular fluid, no role for inhibin in the control of FSH secretion by the pituitary has as yet been defined. This study is addressed to demonstrating the role in inhibin in both male and female rats. In males long time orchidectomized, germinal epithelium or interstitial cell damaged rats will be studied under conditions of inhibin and steroid replacement regimens. In females the model will be ovariectomized rats provided with steroid replacement throughout the estrous cycle and supplemented with inhibin.